Newbie - Altherma Issue

Hi There, I have a Daikin Altherma EKHBH008BB3V3 from 2012 on my site. It has an 'AA' error code on it. I've checked the flow, temperatures and made sure there are no air locks in the backup boiler. I've tested terminals 11&12 along with A1 on K5N contactor. I have 230v on A1, but nothing on 11 or 12. I've then split the connections and found that I have no continuity through the thermal fuse (F1T) which is fitted in the left hand side of the backup boiler. The Klixon (Q1L) is also intermittently working, or not independent of temperature, so must be faulty as well.
I contacted Daikin, but they say that they cannot sell me these parts for 'security reasons', that there is also a built in thermal fuse inside the boiler, and that I have to buy a whole replacement backup boiler to fix it ! This is despite the fact that I have had the boiler running under load by linking the cables across the N/O contact on K5N, so know full well that it works. Has anyone heard this bull***t before? Does anyone know what temperature setting thermal fuse and Klixon that I need to replace these so these I can buy off the shelf replacements elsewhere. Also, do you know the best place to get them from please?